The Health and Human Services Department is considering housing at military bases those children picked up crossing the U.S. border illegally either alone or after being separated from their parents by the government, according to two U.S. officials.

One official said the department is looking at four bases in Texas and Arkansas. The officials discussed the plan Tuesday on condition of anonymity because it has not been made public or made final.

Health and Human Services, which oversees about 100 shelters in 14 states for children who are caught at the border, said in a statement that it routinely evaluates additional locations for temporary housing. It did not elaborate on specific plans.

Health and Human Services takes custody of children who cross the border alone within 48 hours, as well as children who are separated from their families when their parents are charged with crimes or the child’s welfare is in doubt.

During a surge in children from Central America in 2014, Health and Human Services temporarily used military bases in California, Oklahoma and Texas to house children.

The Department of Homeland Security has limited space to house families that are kept together — only about 2,700 beds at three family detention centers in Texas and Pennsylvania. In April alone, people who came as families accounted for nearly 10,000 Border Patrol arrests. Another 4,300 were unaccompanied children.

Nearly 1 in 4 Border Patrol arrests on the Mexican border from October through April was someone who came in a family. That means any large increase in prosecutions will likely cause parents to be separated from their children while they face charges and do time in jail.

Homeland Security Secretary Kirstjen Nielsen defended the Trump administration’s practice of separating children from parents when the family is being prosecuted for entering the U.S. illegally, telling a Senate committee Tuesday that removing children from parents facing criminal charges happens “in the United States every day.”

Nielsen, who has led the agency since December, came under attack from Democratic senators days after Attorney General Jeff Sessions said a “zero tolerance” policy toward people entering the country illegally could lead to more families being split up while parents are prosecuted.

In a contentious exchange with Sen. Kamala Harris, D-Calif., Nielsen said her department was not taking children from parents as a way to deter illegal immigration. Rather, Nielsen said, if a person crosses the border illegally: “We will refer you for prosecution. You’ve broken U.S. law.”

When Harris pressed her about what that would mean for a 4-year-old child whose family faces charges of entering the country illegally, Nielsen said, “What we’ll be doing is prosecuting parents who’ve broken the law, just as we do every day in the United States of America.”

The children are transferred to the custody of Health and Human Services within 48 hours, she said. That department then finds people for the children to stay with while the parents are in custody, she said.

“They will be separated from their parent,” said Harris, who’s considered a possible contender for her party’s 2020 presidential nomination.

“Just like we do in the United States every day,” Nielsen replied.

But she did not dispute criticism by Sen. Claire McCaskill, D-Mo., that the government could do a better job of monitoring the children it places in a family’s custody to make sure they’re safe.

“I could not agree with your concerns more, period,” Nielsen said.

Nielsen told the Senate Homeland Security and Governmental Affairs Committee that her agency and HHS have procedures aimed at making sure the people caring for the children are not criminals.

“It is our duty to protect them, to keep them in a safe environment,” Nielsen said.

DHS has said it would refer all arrests for illegal entry to federal prosecutors, backing up Sessions’ policy, announced last month, to expand criminal prosecutions of people with few or no previous offenses. A conviction for illegal entry carries a maximum penalty of six months in custody for first-time crossers — though they usually do far less time — and two years for repeat offenses.

Just last week, President Donald Trump criticized Nielsen at a Cabinet meeting for not doing enough to stop illegal border crossings. He discounted her explanation that her department faces legal restrictions on what it can do, according to people familiar with the exchange.

The agency has denied a report by The New York Times that the confrontation left Nielsen close to resigning.